Propeller



March 9, 1937. F.3w. CALDWELLy PROPELLER original Filed nay 25, 1929 SSheets-Sheet 1 March 9, 1937. v F. w. CALDWELL PROPELLER Original Filed Mayj25, 1925) 3 Sheets-Sheet 2 March 9, 1937. F. w. CALDWELL PROPELLER Original Filed May 25, 1929 3 Sheets-Sheet 3 ME @REMI/TM Ressued Mar. 9, 1937 UNITED STATES PATENT OFFICE Frank W. CaldwelL Hartford, Conn., assignor, by

mum

tatto United Aircraft C01'- poration. a corporation of Delaware Vorigami No. 1,893,612, dans January 1o, 19:3, serial No. 366.051, my as, 1929. Application for reissue January 9, 1935, Serial No. 1,529

35 Claims.

This invention relates to propellers, and more particularly lto adjustable pitch propellers adapted for aircraft use.

One object of the invention is the provision 5 of a propeller of the character mentioned. the

angle of pitch of the propeller bladesbeing controlled by a simple' system, means being provided for increasing the pitch of the blades while the turning eilect on the blades caused by centrifugal l force is relied on to decrease the blade pitch.

and from the accompanying drawings, in which Fig. 1 is a central section through a propeller,

`embodying the present invention, the fluid pres- ;'5 sure' system being diagrammatically illustrated;

Fig. 2 is a section on the line 2--2 of Fig. l;r

Fig. 31s a section on the line 3 3 of Fig. 1;

Figs. 4 to 7 show a modified form of the invention, Fig. 4 being a central section through a pro- :ru peller, Fig. 5 showing a front elevation, Fig. 6

being a section on the line 6 5 of Fig. 4 and Fig.

'l being a part diagrammatic showing of a. control system;

Figs. B, 9 and 10 show another modification of 35 the invention, Fig. 8 being a central section through a propeller, Fig. 9 being a sectionl von the line 9 9 of Fig. 10, and Fig. 10 being a section on the line Ill-Il of Fig. 9;

Fig. il is a vector diagram showing how ceni" trifugal force during ight tends to turn thelprof peller blades to low-pitch position.

Referring more particularly to the drawings by reference numerals, first with respect to the form of construction shown in Figs. l to 3 inclusive, 4" the propeller l5 comprises essentially the hub Il, blades I2 and il, and the blade retaining device designated generally il. The blade retaining device is shown in the form of a split clamp, the

' semicyllndrical halves of which are bolted to- "0 gether by the bolts l5, forming a barrel with inturned end flanges so that the hollow roots ofthe blades are engaged and retained against the action of centrifugal force. The hollow blade roots are moimted on radial hub extensions. The

v propeller illustrated is of the two bladed type (Ci. 17a-163) and there are therefore two hub extensions l5 and I'I extending into the hollow blade roots, but it will be understood that any desired number of blades may be provided. Between the blade roots and the hub extensions are suitable bearing mem- 5 bers, preferably antlfriction roller members l5. There is preferably a set of antifriction rollers adjacent the outer end of each hub projection, and another adjacent the inner end of the blade root, and the hub projection is preferably tapered l0 in cross sectional dimensions as shown. `Between the inside flange 20 of each of the blades and the split clamp il is a roller member 2l, designed to take the radial outward force exerted on the blade in a substantially frictionlessv manner. The l5 various antifriction members I8 and 2| provide for substantially effortless-adjustment of blades about their longitudinalaxes, while still serving to hold the blade against movement relatively to the hub in any other direction. The propeller 20 hub Ii is splined or otherwise fixed to the hollow engine driven shaft 23. 'I'his shaft 22 may be' the usual crank shaft of the engine which drives the propeller,

In accordance `with the present invention the blade angles are adjusted during flight preferably in accordance with the speed of the engine. This adjustment of the blade angles is accomplished, as shown, by a hydraulic pressure system, comprising the hollow propeller shaft 23 containing 30 a quantity of oil or other liquid 2l. The pressure of this oil is controlled automatically and may also be controlled manually in a manner to be presently described. -The pressure of the oil is ef.- fective on a pressure responsive element, preferably a piston 25, operating ina cylinder 26, shown vat the forward end of the propeller shaft. The

piston 25 is fixed to the end of a piston operated member or tube 21 which is slidably mounted within the hollow propeller shaft, and which is open at its ends so that the space between the piston 25 and the cylinder head 281s maintained in constant communication with the oil in the hollow shaft 23. Leakage around the outside of the tube 21 may be prevented by a suitable 45 packing or washer 29, and packing material III is also provided between the piston 25 and the cylinder 25.

The piston 25 is yieldlngly urged` outwardly by a series of compression springs 5I extending be- 50 tween the piston 25 and the inner end of the cylinder 25. The force exerted by these springs, however. is very small as compared to theautward force on the piston produced by the axial turning tendency of the blades caused by centrifugal force, and which constantly tends to cause a decrease in the pitch of the blades. This centrifugal force eiect or tendency of the blades to reduce their pitch is proportional to the diiference 5 of the moments of inertia about the two principal increase in pitch being caused by increase inthe iluid pressure acting on the piston shown in Fig. 1.

This arrangement provides a very simple pitch controlling mechanism.

Centrifugal force acts rradially through the axis of revolution. See Fig. 1l. Considering the force acting on small particles at a and b this force may be resolved into a vector parallel to the axis of pitch adjustment, and one normal to the axis of pitch adjustment. The vector 2.0 parallel to this axis of the pitch adjustment cannot cause torsion about this axis. If the vectors normal to the axis of pitch adjustment are transferred to a sectional View at A-A it will be obv'lous that they will tend to decrease the pitch of the fblade. It may be shown mathematically that this force is equal to /gW2 (I ma-I min.) sin a cos adn. Where t is the density of the material in weights units, g the acceleration due to gravity, I maj. and I min. the principal moments of inertia plane of rotation and the axis of leastinertia. Ii his quantity is integrated for the full length of the blade it may be shown that the resultant twisting moment is of a considerable magnitude. It has a value between 2000 pounds inches 'and 3000 pounds inches per blade for a number of propellers of usual slzesand speeds.

When the pitch of the propeller in operation is not changed by force of the hydraulically driven piston, it is held by centrifugal force in the lowest pitch position that it can assume. 'I'his may be called its normal pitch, because that is the pitch the blades have except as purposely chan/ged by the pilot through force of the hydraulic cylinder. On the piston operated member 21 are two lugs 32' and 33 to which are pivotally connected 4 links 34 and 35 respectively. These links extend out through suitable slots 3B Ain the cylinder 26 and in turn are pivotedyto arms 31 and 3B each of which is connected to the flanged inner end of a propeller blade. The arms 31 and 3B as shown are xed directly to the blade flange by means of screws 39 or the like, the split lamp being cut away or slotted in such a way as to provide for the pitch adjusting' arms mentioned, these slots being indicated at 40. l

The arrangement of the link connection between the reciprocally operable control member or piston and the blades is a simple but very desirable formof interconnection, as the arms 31 and 38 and the links 34 and 35 provide what might be termed toggles so arranged as to produce very small angular movements of the blades about the blade axes upon substantial range of movement of the piston tube. This gives the piston a consider- "able leverage and permits the use of moderate oil,pressures with la comparatively small piston area. A further advantage of this linkage is that the sliding members are not subjected to side loads, the heavy loads being applied on the pivots of the links so that the operating friction is reduced to a minimum. I

It will now be apparent that when the piston operated member or tube 21 is moved in the direction of its length, the lugs`32 and 33, will be of the cross section, and a'the'angle between the* moved closer to or farther from the propeller blades, thus shifting both blades to simultaneously increase or decrease their pitch. When the tube 21 is moved inwardly by the increase of pressure of the oil in the system, the pitch of the blades is increased. The oil pressure isl opposed by the springs 3|, and also by the large centrifugal force on the blades themselves tending to decrease their angles of incidence, the cross section of the blades being so designed that the centrifugal turning tendency of the blades to reduce their pitch is very substantial.

'I'he .uid pressure in the fluid system is gen` erated preferably by an engine driven pump. As

shown in Fig. l this pump 53 is connected by suit- Y able gearing 43 to an engine driven gear 44 which may be fixed on the shaft 23. The pump is of the intermeshing gear type for example, and is supplied with oil through a supply conduit 44 which leads to the sump of the engine crank case, this sump being designated diagrammatically at. 45. 'I'he engine oil forced out of the pump` ilows through the pipe 46 to pipe 41 which is in constant communication with-the inside of the shaft 23. Preferably the latter is provided with a series of openings communicating with an annular supply passage 48in the packing part 49. As shown. the oil chamber in the engine yshaft 23 is closed at 50. I

Connected with the pipe 45 is a relief valve 52 adapted to return the oil passing through the pump 53 through a variable valve restriction 54 to the engine sump. The size of the opening at` 54 is controlled by a suitable adjustable screw 55 or the like. When this screw 55 is in such a position as to considerably restrict the sizeof the opening 54. the pressure on the output side of the pump is increased.- Thiscauses the piston tube to be forced inwardly thus moving the propeller blades about theirlongitudinal axes and increasing their pitch.

For a given setting of the by-pa'ss the oil pressurejwill be nearly proportionateto the square of the engine speed and the centrifugal twisting moments on the blades will be proportional to the square of the engine speed so that these -two opposing forces will just about balance at various engine speeds unless the restriction of the orice is altered.

An increase in pitch of the blades causes the engine to do more work and consequently decreases the speed of the engine. The engine speed andthe pitch of tne propeller blades may be manually controlled, and these factors are also automatically controlled in sucha way as` to normally maintain the engine speed substantially constant where it can operate at its most efficient speed, the pitch of the blades varying as the speed of the airplane changes. For example the screw 55 may be connected by a suitable cable to a fly ball governor or the like responsive to the speed of the engine. The engine being directly connected to the propeller operates at the propeller speed, so when the airplane increases its speed, by diving for example, the load on the engine would be decreased and it wouldI speed up. possibly to an injurious high speed were it not for the automatic control herein provided. In accordance with the present invention should `the airplane dive and the load on the engine tend to fall oithe engine tends to increase its speed;

restriction in the by-pass and a further increase in oil pressure. The piston tube therefore is lorced to the right, the pitch of the blades is increased, thusincreasing the load on the engine. The engine speed-therefore is maintained substantially constant 4during the vari/ous maneuvers of the airplane unless it is desired to manually efi'ect the control of the engine speed. The proper engine speed for any particular circum-l stance may be chosen, and the blade angles automatically controlled so that both the engine and the propeller Voperate at their maximum emciencies.

The form of. construction shown in Figs. 4 to 7 inclusive is generally similar to the device which has just been described. .The hollow engine shaft 00 formsa support for the propeller hub 6| on which are mounted the blades 02 and 03 in a manner similar to the propeller construction previously described. 'The fluid pressure element or piston, in this case, is shown adapted for operation within the hollow shaft 00, piston 04 being lconnected to the piston operated member 0l which is pivotally connected to the two links 01 and 00 at its forward end which extends ,25 through a packing bushing 60. These two links 01 and 68 in turn are pivotally connected to arms l00 and 10 fixed to the inner flanged portions of the blades. As the pressure on the oil supply 1| at the rear oi' the piston 64 increases, the piston and its operated member 65 move to the left as viewed in Figs. 4 and 6, thus swinging the arms 09 and 10 and adjusting the pitch of the propeller blades to increase their pitch equal amounts. When the fluid 'pressure falls the centrifugal force'acting on the blades themselves returns the blades towards minimum pitch positions to an extent determined by the iluid pressure.

The oil or other fluid 1| is supplied to the inside of the hollow shaft 60 through a supply passage 13 extending from the oil pump 14 which may be directly connected tothe engine shaft 00 as indicated in Fig. 4. Oil is supplied from the engine sump 15 and is forced by the pump 14 to the shaft 60, some of the oil by-passing the valve 10 and returning through the passage 11 to the sump. The amount of opening of the valve 10 is determined by a valve needle suitably ilxed to a piston 10 contained in the cylinder 19, the upper side of the piston .being in communication with the outlet side of the pump through pipe 80. As the pressure on the outlet side of the pump increases the valve controlling piston 18 is forced down against the adjustable spring to restrict the opening 16 and thus cause an increase in the pressure oi' the fluid supplied to the hollow shaft 00. It will be apparent that as the by-pass is restricted, the fluid pressure on the piston 64 is increased, and this causes an increase in pitch of the propeller blades. This increase in pitch of the propeller blades by throwing more load on the engine serves to maintain the engine speed substantially constant through various maneuvers of the airplane.

of the engine, or change the angle of the propeller blades, the setting` of the valve 16 may be manually aflected by operation of the control cable 02 extending to the pilots cockpit, this cable passing into the valve case at 03 and extending around an operating pulley 04 threaded on the screw 05 and forming an abutment for one end of the spring 00 which balances the pressure on the upper side of the controlling piston 10. The varia- 75 tion in the pressure of the spring 06 may therel matic control.

When it is desired to manually check the speed fore be manually controlled to effect the control of the iluid pressure inf the system..

Y The by-pass valve shown in Fig. 4 may be replaced as shown in Fig. '7 by a controllable valve 00 which is adapted to be controlled by a manually operable thumb screw 0| in threaded engagement with the longitudinally adjustable screw 02 fixed to the extension spring 03. This spring is connected to a pivoted lever 94. the spring pressure being balanced against the centriiugal action of the ily ball governor 95 which is operably connected to the engine by suitable gearing 00. The ily ball governor operates to maintain a substantially constant engine speed for any particular setting oi the thumb screw 0|. causing the adjustment of the blade angles in an automatic manner during various maneuvers of the airplane. The manual adjustment at 9| permits variation ol the engine speed as desired and forms a manual control which modifies the auto- As shown in Figs. 8, 9 and 10, the propeller |00 embodies the blades |0| and |02 rotatably mount ed on the radial hub projections |00 and |04 respectively in the manner generally similar to the forms of construction previously described. The radial hub projections |03 and |04 instead of projecting from a hollow hub member, are formed as outward radial extensions on the engine operated shaft |05.

Projecting inwardly from the flanged ends o`f the blades |0| and |02 are posts |01 and |00, the inner ends of which are pivotally connected to operating arms |09 and ||0 respectively. These arms are pivoted to the outer end of a piston operated rod ||I controlled by the fluid pressure responsive member or piston ||2.v The latter operates in a cylinder formed by the hollow engine shaft |05, 'and this cylinder is provided with a series of relief passages 3 through which the oil in the chambers ||4 and '||5 on oppositeA sides of the piston may be relieved and return to the engine sump ll6. Oil is pumped from this sump'by the pump I1, and the outlet side of the pump is connected to the two pipe branches H8 and ||9 extending to the chambers or spaces ||4 and ||5 in the engine shaft:v Embracing the vented portion of the shaft |05 is asleeve valve |2| having a cut-away portion |22 of a width approximately the same as the width of the piston ||2 so that the sleeve |2| together with a piston ||2 can close all of the valve openings H3 when the system is in stable equilibrium. If the valve |2| is moved to the left as viewed in Fig. 8 the oil pressure ln the chamber ||4 reduces, the oil flowing out of this chamber through one 0r more openings IIS which are uncovered at the time by the sleeve |2|. Oil tends to ilow from the pump into the chamber ||5 on the opposite side oi' the piston to force the piston ||2 to the left and again cover up .the passage ||3 which was opened. 'I'his occurs until the piston ||2 has been moved farenough to the left to stabilize the system again and equalize the pressures on opposite'sides of the piston for the new setting of the valve sleeve, the movements of the piston spring |21 having an adjustment nut |20 tends to hold the sleeve I2| in the position shown in Fig. 8 corresponding to the minimum pitch position of the propeller blades. The pump shaft |30 which is driven from the engine shaft controls 5 -a fly ball governor I3I which automatically affects the position of the bell crank lever |32 connected by link |33 to the sleeve IZI. If the engine speed tends toincrease, the link |33 is automatically moved to the left, thus causing a movement of 10 the piston rod I I I to the left to effect an increase in pitch of the propeller blades. As this tends to increase the load on the engine it will be apparent -thatthe engine isy automatically controlled so that its speed is normally maintained substantially constant during various airplane maneuvers. The automatic control may be overcome in a manual manner whenever desired by operation of the l'ever |25 so that the speed of the motor can be adjusted to the desired value for any special occasion. y

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus,

` and that changes may be made therein without tatable on their longitudinal axes but otherwise immovable relative to the hub, a drive shaft carrying the.v hub and having an axial bore, a source of hydraulic pressure in communication with the bore, an enlarged cylinder mounted on the hub and extended beyond the forward end of the engine shaft, and positioned beyond the blades, a piston in the cylinder having a` tubular extension slidably fitted in the engine shaft bore and 40 opening through the piston', the walls of the cylinder near its base having diametrically disposed longitudinal slots, links pivotally `connected to the piston extending through said slots and pivotally connected to arms laterally extending from the 45 roots of the blades whereby to rotate the blades on their longitudinal .axes to increase their pitch, and means to control hydraulic `pressure in the cylinder and so to control increase of pitch due to movement of the .piston` 50 2. An aeronautical `controllable `pitch propeller,

comprising a hub, blades mounted thereon rotatable on their longitudinal axes but otherwise immovable relative to the hub, a drive shaft carrying the hub and having an axial bore, a source of 55 hydraulic pressure` in communication with the bore, an enlarged cylinder `mounted on the hub and extended beyond the forward end of the engine shaft, and positioned 'beyond the blades, a piston in the cylinder having a tubular exten- 6o sion slidably fitted in the engine shaft bore and opening through the piston, the walls of the cylinder near its base having diametrically disposed longitudinal slots, links pivotally connected to the piston extending through said slots andpivotally n3 connected to arms laterally extending from the roots of the blades whereby to rotate the blades on their longitudinal axes to increase their pitch, springs in the cylinder opposing movement of the piston by hydraulic pressure but adapted to To be'overcome thereby to a degree depending on the hydraulic pressure applied to the cylinder, and

means to control hydraulic pressure in the cylincomprising a hub, blades mounted thereon rotatable on theirlongitudinal axes but otherwise immovable relative to the hub, a drive shaft carry- `ing the hub and having an axial bore, a source of hydraulic pressure in communication with the bore, an enlarged cylinder mounted on the hub and extended beyond the forward end of the engine shaft,` a piston in the cylinder having a tubular extension slidably fitted in the engine shaft bore and opening beyond the piston, the walls of the cylinder near its base having diametrically disposed longitudinal slots, toggle links pivotally connected to the piston extending through said slots and pivotally connected to arms laterally extending from the'roots of the blades, and hand-operated means to control hydraulic pressure in the cylinder to increase the pitch of the blades.

4. An aeronautical controllable pitch propeller. comprising a hub, blades mounted thereon rotatable on their longitudinal axes but otherwise immovable relative tothe hub, a drive shaft carrying the hub and having an axial bore, a source of hydraulic pressure in communication with the bore, an enlarged cylinder mounted on the hub and extended beyond the forward end .of the engine shaft, a piston inthe cylinder having a tubular extension slidably fitted in the engine shaft bore and'opening beyond the piston, the walls of the cylinder near its base having diametrically disposed longitudinal slots, toggle links pivotally *connected to the piston extending through said slots and pivotally connected to arms laterally extending vfrom the roots of the blades, springs in the cylinder opposing movement of the piston by hydraulic pressure but adapted to be overcome thereby to a degree depending on the hydraulic pressure applied to the cylinder, and hand-operated means to control hydraulic pressure in the cylinder to increase the pitch of the blades.

5. An aeronautical variable pitch propeller and control mechanism therefor, comprising a hub, blades mounted thereon rotatable on their longitudinal axes but otherwise immovable relative to the hub, an engine drive shaft carrying the hub and having an axial bore, a source of hydraulic pressurerin communication with the bore, an enlarged cylinder mounted on the hub 1 and extended ybeyond the forwardy end of the 6. `An aeronautical variable pitch propeller and control mechanism therefor, comprising a hub,

blades mounted thereon rotatable on their longi,

tudnal axes but otherwise immovable relative to the hub, an engine drive shaft carrying the hub and having an axial bore, a source of hydraulic' pressure in communication with the bore, an enlarged cylinder mounted on the hub and extendedl beyond the forward "end of the engine shaft, a piston in the cylinder having a tubular extension slidably fitted in the engine shaftv bore and opening through the piston, the walls of the cylinder near its base having diametrically disposed longitudinal slots, links pivotally connected to the pistonextending through said slots and pivotally connected to arms laterally extending from the roots of theblades, springs in the cylinder opposing movement of the piston by hydraulic pressure but adapted to be overcome thereby to a degree depending on the hydraulic pressure applied to the cylinder, and automatic means governed by speed of rotation of the shaft to increase the hydraulic pressure in the cylinder with increase of shaft speed.

7. An aeronautical propeller and mechanism for increasing its pitch in night, comprising a hub, blades mounted thereon rotatable on their longitudinal axes but otherwise immovable relative to l5 the hub, an engine drive shaft carrying the hub and having an axial bore, a source Vo1' hydraulic pressure in communication with the bore, an enlarged cylinder mounted on the hub and extended beyond the forward end ofthe drive shaft, a piston in thecylinder having a tubular extension slidably fittedY in the shaft bore and opening through the piston, the walls of the cylinder near itsbase having diametrically disposed longitudinal slots., toggle links pivotally connected to the piston extending through said slots and pivotally connected to arms laterally extending from the roots of the blades, automatic means governed by.

speed of rotation of the shaft to increase the hydraulic pressure in the cylinder with increase of shaft speed, and hand operated means to control hydraulic pressure in the cyllnderindependently of and in spite of the automatic governing control thereof.

`8. An aeronautical propeller and mechanism for increasing its pitch in flight, comprising ar hub, blades mounted thereon rotatable on their longitudinal axes but otherwise immovable relative to the hub, an engine drive shaft carrying the hub and having an axial bore, a source of hydraulic pressure in communication with the'bore, an enlarged cylinder mounted on the hub and extended beyond the forward end of the drive shaft, a piston in the cylinder having a tubular extension slidably tted in the shaft bore, and opening through the piston, the walls of the cylinder near its base having diametrically disposed longitudinal slots, toggle links pivotally connected to the piston extending through said slots and pivotally connected to arms laterallyA extending from the roots of the blades, springs in the cylinder opposing movement of the piston by hydraulic pressure but adapted to be overcome thereby to a degree depending'on the hydraulic pressure applied to the cylinder, automatic means governed by speed of rotation of the shaft to increase the hydraulic pressure in the cylinder with increase#i of shaft speed, and hand operated means to control hydraulic pressure in the cylinder independently of and in spite `of the automatic governing control thereof.

9. An aeronautical propeller adapted to have its blades held in normal low-pitch position by centrifugal force acting on the mass of the blades, and controllable means to increase the pitch of the blades in iiight, said means comprising a fluid pressure system including a pump driven by the engine, a drive shaft, a hub on the drive shaft, blades mounted on the hub and adapted to be rotated thereon to adjust their pitch, the shaft having a cylindrical bore at its forward end closed by a terminal nut, a piston slidably mounted in the bore, a rigid stem extending through the nut from the piston, toggle links pivotally attached to increase the pitch of the blades upon forward driving of the piston by hydraulic pressure in the cylinder.

10. A variable-pitch propeller having a normal low-pitch and adapted to have its pitch increased in flight by hydraulically-operated control means, comprising blades with hollow flanged roots, a hollow drive shaft carrying radial hub projections at its forward end adapted to receive the blade roots, a split internally flanged barrel engaging the said flanges for holding the blades on the hub projections, a piston mounted in the hollow shaft, a rod extending forward from the piston, toggle links connecting the forward end of the rod to the roots of the blades whereby forced travel of the piston causes rotation of the blades on their longitudinal axes, a source of hydraulic pressure connected to the cylinder, and means to control the pressure in the cylinder and thereby`to vary the pitch of the propeller in iiight.

11. A controllable pitch aeronautical propeller comprising a hollow drive shaft forming apressure cylinder at its forward end, lateral integral hub projections from the forward end of the cylinder, blades mounted on the projections and adapted to be rotated on their longitudinal axes for pitch adjustment in flight, a piston mounted in the pressure cylinder, a rod extending from the piston through the forward end of the pressure cylinder and linked to crank arms on the blade roots, a source of hydraulic pressure connected to each end of the pressure cylinder, escape vents in the cylinderwall, anda slidable external valve surrounding the drive shaft and controlling the escape vents to determine a balanced position of the piston in the cylinder, whereby to control the pitch of the blades in flight by position of said valve.

peller comprising a hollow drive shaft forming an integral pressure cylinder at its forward end, a hub carried on the shaft, blades mounted in the hub and rotatable therein on Atheir longitudinal axes, a piston mounted in the pressure cylinder, a rod] extending from the piston through the forward end of the pressure cylinder, links connecting the rod to crank arms on the blade roots, a source of hydraulic pressure connected to each end of the pressure cylinder, escape vents in the cylinder wall, a slidable external valve controlling the escape vents and so determining the position of the piston in the cylinder,- and manually-operable means to shift the valve at will, whereby to control the pitch of the blades in ight.

13. A controllablepitch aeronautical propeller comprising a hollow drive shaft forming a pressure cylinder at its forward end, lateral integral hub projections from the forward end of the cyl'- inder, blades with hollow roots mounted on the projections, the blades having external terminal flanges, a split barrel with inturned end flanges enclosing the flanged roots of the blades and retaining them against longitudinal movement, anti-friction bearings between the blades and the hub projections and between the blades and the barrel, a piston mounted in the pressure cylinder, a rod extending from the piston through the forward end of the pressure cylinder, links connecting the rod to crank arms on the blade roots, a source of hydraulic pressure connected to each end of the pressure cylinder, escape vents in the cylinder wall, and a slidable external valve controlling the escape vents and so providing 12. A controllable pitch yaeronautical pro- .i ing external terminal anges, a split barrelwith inturned end flanges enclosing the flanged roots of the blades and retaining them against longitudinal movement, anti-friction bearings between the blades andthe hub projectionsiand l between the blade anges and the barrel anges, a piston mounted in the pressurev cylinder, a rod extending from the piston through the forward end of the pressure cylinder, links connecting the rod to projections on the blade roots whereby to change the pitch of the blades when the pistou is moved, a source of hydraulic pressure connected to each end of the pressure cylinder, escape vents in the cylinder wall, and a slidable external valve controlling the escape vents and adapted to provide a balanced intermediate position of the piston in the cylinder and so to control the pitch of the blades.

15. A variable-pitch propeller, having a normal low-pitch and adapted` to have its pitch increased in ight by hydraulically-operated control means, comprising blades with `hollow flanged roots, a hollow engine shaft having hollow integral radial hub projections at its forward end adapted to receive the blade roots, external means engaging the said flanges for holding the blades on the hub projections, a piston slidably mounted in Van axial bore in the engine shaft,

a rod extending forward from the piston through the endof the shaft, links extending from the 40 forward end of the rod to extensions from the roots of the blades whereby forced travel of the piston causes rotation- `of the blades on` their longitudinal axes, aisource of hydraulic pressure connected to the cylinder on yeach side-of the piston, relief vents through the cylinder walls, a sleevevvalve surrounding the vented portion of the cylinder and adapted to be moved to control the said vents to determine a balanced position of the piston in the cylinder and so to control the pitch adjustment of the blades.

l6. An aeronautical propeller comprising a drive shaft having a bore therein, a source of hydraulic pressure connected to the bore, a hub fixed on the drive shaft and comprising lateral radial blade-receiving projections, blades having hollow flanged roots adapted t`o ilt over the hub projections and to be rotatably mounted thereon, a split barrel having inturned end flanges adapted to enclose the blade root flanges 00 and hold the bladesI against longitudinal displacement, a pressure cylinder aligned with and connected to the bore of the drive shaft, a movable piston` in the cylinder, toggle connections from the piston extending forwardfof the hub a5 to the blades'whereby to` turn the blades on the huh projections upon actuation of the piston, and means'to control fluid pressurein the cylinder whereby to drive the piston to increase the pitch of the-blades while in operation.

l'l. A controllable pitch propeller comprising a hub, blades journalled on the hub and constructed and arranged so thatl they will be turned in the direction to decrease their pitch angle by centrifugal force produced by rotation of the propeller, 15 aplston,means connecting the piston to the blades,

and means for introducing liquid under pressure. onto one side of said piston, to overcome the pitch changing action of centrifugal force on said blades and turn the blades to increase their pitch angle.'

18. A controllable pitch propeller comprising a hub, blades journalled relative to said hub, a hydraulic piston operatively connected with said blades, means for introducing hydraulic pressure onto one side of said piston to turn the blades on their journals to increase their pitch angles, means for relieving said hydraulic pressure, means including said journals connecting said blades to said hubs to cause centrifugal force produced by rotation of said propeller to decrease their pitch angle when said pressure is relieved.

19. In combination, a hollow drive shaft, a hub driven by said shaft, blades journalied relative to said hub. a hydraulic piston operatively connected v tion between said shaft and said piston, said blades being turned by centrifugal force produced by rotation of said propeller to decrease their pitch angle when said pressure is relieved. y

20. 'An aeronautical engine driven propeller having blades held in low pitch position by centrifugal force acting on the mass of the blades. and controllable means to increase the pitch of theblades in flight, said propeller and means comprising a, hydraulic pressurelsystem including a piston and cylinder assembly and apump driven by the engine, a drive shaft, a hub on the drive shaft, blades mounted-on th'e hub and adapted to be rotated thereon to adjust their pitch, an operative connection between said piston and said blades and a valve for controlling the now of liquid between said pump and said piston, said piston acting to overcome the pitch changing effect of said centrifugal force and turn the blades vto increase their'pitch upon an increase of pre governed by the speed of rotation of said shaft to increase the hydraulic vpressure on the piston I with increase of shaft speed and to relieve said hydraulic pressure with decrease of shaft speed, said blades constructed and arranged to be turned by centrifugal force produced by rotation of said propeller to decrease their pitch angle when said pressure is relieved.

22. In combination an engine driven shaft, a

` propeller having blades operably 'connected to said shaft, a, hydraulically operated piston operably connected with said blades, means for introducing liquid under pressure to one side of said piston to turn the blades to increase their pitch angles, means for governing the ow of liquid to and from said side of said pistoncomprising automatic means governed by the speed of rotation of said shaft to cause liquid to flow to said piston upon an increase of shaft speed, means connecting said blades with said shaft for preventing radial movement of said blades and causing said blades tobe turned and liquid forced from said piston by centrifugal force produced by rotation trolling said pressure comprising automatic means l sure of said liquid on said piston, means connecting said hub and said blades to causecentrifugal force produced byv rotation of said propeller to decrease their pitch angle when said pressure isr reduced.

24. A variable pitch propeller comprising a plurality of blades, means for rotating said blades, liquid pressure operated means for increasing the pitch of said blades, a governor actuated by rotation of said blades above and below a selectedV rate of rotation for controlling the operation of said liquid pressure operated means, means for selecting the said rate of rotation, means associated with said blades for determining the axis of pitch changing movement and the pitch changing effect of centrifugal force and causing said blades to be turned and liquid forced from said liquid pressure operated means by the components of centrifugalv force lying in planes normal to said axis and producedby rotation of said blades when the governor is actuated by a rate of rotation below the selected rate.

25. A controllable pitch propeller comprising a hub, blades journalled relative to the hub, a liquid pressure operated device operatively connected with said blades, a single conduit leading from said device, means for supplying liquid to said device through said conduitrto overcome the action of centrifugal force and turn the blades to increase their pitch angle, and means for draining liquid from said device through said single conduit, said blades constructed and arranged so that centrifugal force produced by rotation of said propeller turns said blades to decrease their pitch angle and forces liquid from said device f through said single conduit.

26. A controllable pitch propeller comprising a hub, blades rotatably mounted relative to the iii) hub, and turned in one direction to change their pitch angles, by centrifugal force produced by rotation of the propeller, resilient means acting on said blades to assist said centrifugal force in turning said bladesa piston, means connecting the piston to the blades, and means for introducing liquid under pressure onto one side of said piston to overcome the pitch changing effect of said centrifugal force and said resilient means, and to turn the blades in the opposite direction.

.27. In combination, an engine driven shaft, a propeller having blades operably connected to saidshaft, an hydraulic piston Ioperably connected with said blades, means for introducing hydraulic pressure onto one side of said piston to turn the blades to increase their pitch angles, t means for controlling said pressure, comprising automatic means governed by the speed of rotation of said shaft to increase the hydraulic pressurel on -the piston with increase oi' shaft speed and to relieve said hydraulic pressure with decrease of shaft speed, springs opposing movement of said piston by hydraulic pressure, and assisting centrifugal force produced by rotation of said propeller to decrease the blade pitch angle when said pressure is relieved.

28. A variable pitch propeller comprising a plul5 rality of blades, means for rotating said blades,

liquid pressure operated means operably connected with said blades for increasing the pitch of said blades, a governorV for controlling the operation of said liquid pressurfeoperated. means, said governor being actuated by rotation of 'said blades above a selected ,rate of rotation to render said liquid` pressure operated means operative to increase the pitch of said blades, means adjustable during operation of saidpropeller for selecting the said rate of rotation, said blades being turned and liquid forced from said liquid pressure operated means by'centrifugal force produced by rotation of said blades when the governor is actuated by a rate of rotation below the selected rate.

29. A controllable pitch propeller comprising, in combination, a hub, blades rotatably mounted relative to said hub, and movable in one direction, to change their pitch angles, by'centrifugal force produced by rotation of the propeller, liquid pressure operated means, means connecting said liquid pressure operated means to said blades, means for introducing liquid under pressure into said liquid pressure operated means to turn the blades in the opposite direction, resilient means opposing movement of said liquid pressure operated means and assisting said centrifugal force to turn said blades in said one direction.

30. In a controllable pitch propeller, incombination, blades movableto low pitch by centrifugal force produced by rotation of the propeller,

liquid pressure operated means, means connecting the liquid pressure operated means to the blades, and means for introducing liquid -under pressure onto one sideV of said liquid pressure operated means, to overcome the action of lcentrifugal force tending to move the blades to low pitch, and to move the blades in the `opposite direction.

31. In a controllable pitch propeller, in combination, a hub, blades journaled relative to said hub, liquid pressure operated means connected with said blades, means for introducing liquid under pressure onto one side of said liquid pressure operated means to turn the blades on their' journal, to increase their pitch angle and to hold the blades at said increased pitch, means for relieving said pressure, said blades constructed and arranged so that centrifugal force produced by rotation of said propeller will decrease their pitch angle when said pressure is relieved.

32i A controllable pitch propeller comprising, a hub, blades journaled on the hub, and movable in the direction to decrease their pitch angle only by centrifugal force produced by rotation of the` propeller, a piston, means connecting the piston to the blades, and means for introducing liquid under pressure onto one side of said piston to overcome the action of centrifugal force tending to decrease the blade pitch and to turn the blades in the opposite direction.

33. A controllable pitch propeller comprising,l

in combination, a'hub, blades journaled for rotation relative to the hub and movable to and held and means for relieving said hydraulic pressure to move the blades toward low pitch, said blades being turned by centrifugal force produced by rotation of the propeller when said pressure is relieved.

34. A controllable pitch propeller comprising, in combination, a hub, blades rotatably mounted relative to the hub and movable to lovv pitch by centrifugal force produced by rotation of the propeller, resilient means acting onsaid blades to assist said centrifugal force in moving said blades, liquid pressure operated means, means connecting the liquid pressure operated means to the blades, and means for introducing` liquid under pressure on one side of said liquid pressure operated means to overcome the action of said l0 resilient means and the action offcentriiugal i'orce tending to move the blades to lowpitch and to move the blades .in the opposite direction.v

35. In a controllable pitch propeller, in combiy nation. liquid pressure operated meanspropeller blades movable to low pitch by centrifugal force produced by rotation of the propeller when said liquid pressure means is inoperative, means con-` necting the liquid pressure operated means to the blades, a governor responsive to changes from a selected rate of rotation, and means controlled by said governor for introducing liquid under pressure onto one side of said liquid pressure operated means to overcome the action o! centrifugal force tending to move the blades to lowpitch and to move the blades in the opposite direction. e v

FRANKNV. CALDWELL. 

